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Monitor the system of 120/240V or 120/208V in North America

Monitoring Solar PV Output with WEM3080T Phase C in 120/240V or 120/208V Systems

Background: 120/240V or 120/208V Systems

In North America, both 120/240V and 120/208V systems are prevalent:

  • 120/240V: A single-phase 3-wire system with two L lines and one neutral line, where the two high legs are 180 degrees out of phase.
  • 120/208V: A two-phase configuration in a 3-phase system, containing two L lines and one neutral line, where the two high legs are 120 degrees out of phase.

Method: Monitoring a Single High Leg and Doubling the Reading

Starting from version 98.70, we introduced the "ctcratio" parameter.

In both 120/240V and 120/208V systems, the solar inverter output and grid each contain two high legs. In theory, monitoring both grid and solar in a single energy meter would require four input channels.

However, considering the balanced nature of solar output, it's noteworthy that the two high leg outputs tend to be nearly identical.

Understanding "CTCratio" Parameter

By measuring just one high leg of the solar inverter output (Phase C) and doubling its reading, the total solar inverter output can be estimated. The "CTCratio" parameter, introduced since version 98.70, enables doubling the reading of Phase C.

When using Phase A and Phase B to monitor the grid and Phase C to monitor one high leg of the solar PV, setting "CTCratio" to '2' doubles the readings (current, active power, KWh) of Phase C.

WEM3080T in 120/240V or 120/208V system

Setting "CTCratio" to '2' for Doubling Phase C Reading

Adjust the "CTCratio" value through the API (/api/ctcratio?x=value). By default, this value is set to '1'. Changing it to '2' doubles the readings of Phase C, including current, active power, forward KWh, and reverse KWh.

For resetting to default, simply set "CTCratio" back to '1'.

For detailed instructions, refer to New parameter (CTCratio).

Operational Steps

  1. Install a WEM3080T.
  2. Utilize Phase A and Phase B for monitoring the two high legs of the grid. Use Phase C to monitor one high leg of the solar inverter output.
  3. Set the "CTCratio" to '2'.


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